The present invention generally relates to a membrane switch, and more particularly, to a membrane switch having a hemispherical metal click spring.
An example of conventional membrane switch of this kind is described with reference to FIG. 5 and FIG. 6.
As shown in the figures, a membrane switch 1 includes a circuit board 2, a center fixed contact point 3 and side fixed contact points 4 provided on the circuit board 2, a click spring 5, and an insulation sheet 7, adhered on the circuit board 2, with the top face of the click spring 5 included thereunder, with adhesive material 6.
The circuit board 2 is made of a film such as polyester. The center fixed contact point 3 is provided at the center of the circuit board 2, and the side fixed contact point 4 having an almost round shape is provided in the surrounding area around the center fixed contact point 4. The click spring 5 is made of hemispherical metal, and operates as a movable contact. This click spring 5 is provided so that its bottom peripheral portion is attached to the side fixed contact point 4, and its center portion touches the top face of the center fixed contact point 3.
Furthermore, the insulation sheet 7 is adhered on the circuit board 2 with adhesive material 6. Since the insulation sheet 7 is also adhered on the click spring 5 with adhesive material 6, the click spring is stationed not to slip.
Accordingly, by pressing a key top (not shown) positioned on top of nearly-center portion of the click spring 5, the insulation sheet 7 and the click spring 5 are pushed downward. The center portion of the click spring serving as a movable contact touches the center fixed contact point 3, and conducts electricity between the center fixed contact point 3 and the side fixed contact point 4.
The abovementioned click spring 5 is stationed not to slip by adhesion of the insulation sheet 7. As shown in FIG. 5 and FIG. 6, a nearly-round air bleeder hole 8 is provided to the insulation sheet 7 by opening an edge of the click spring 5 in order to release air when the click spring 5 is pressed.
The air bleeder hole 8 provided to the membrane switch 1 according to the conventional example described above is provided in a way a portion of the click spring 5 is exposed. It has been a problem that, because the air bleeding hole 8 is close to the fixed contact points 3 and 4, dust and moisture are easy to enter, and the function as a membrane switch is lowered.
The present invention is made to solve the technical problem described above. It is the object of the present invention to lower, under the configuration in which the click spring is stationed at a fixed position, the bad effect caused by the dust and the moisture entering through the air bleeding hole of the abovementioned conventional example.
The present invention is made to achieve the above object. A membrane switch relative to the present invention includes fixed contact points on a circuit board made of a film of resin material, movable contact point member made of semi-spherical metal click spring touching said contact points, and an insulating sheet adhered on said circuit board with said click spring inclusive, characterized by a continuous air path connected to a portion of said click spring, formed as a portion where no adhesive material is placed, between said insulating material adhered on a top face of said click spring and said click spring, and said continuous air path is connected to openings formed between an edge of said insulation sheet and an edge of said circuit board.
The membrane switch is characterized by said openings are located on both edge opposite to each other of said circuit board, and said continuous air path formed with a stripe pattern reaches to said openings on both edge opposite to each other. The membrane switch is further characterized by said continuous air path is formed by adhering said insulation sheet to said circuit board with a top face of said click spring inclusive with a spot pattern, and said continuous air path is connected to said openings. The membrane switch is yet further characterized by said continuous air path is formed by adhering said insulation sheet to said circuit board with a top face of said click spring inclusive with a matrix pattern, and said continuous air path is connected to said openings.